Chucks of the Jacobs type are known having a chuck body on which a plurality, usually three, of jaws is radially, and normally also axially, displaceable for clamping a tool or even a workpiece. A standard such chuck, such as shown in my earlier U.S. Pat. No. 3,938,817 or in German utility model 7,524,037, has a sleeve rotatable relative to the chuck body to effect this radial displacement of the jaws, normally by means of mating screw threads on the sleeve and on the jaws.
It is a known procedure to tighten such a chuck by means of a key. To this end the rim of the tightening sleeve is formed with teeth so that it constitutes an annular axially facing gear, and the chuck body is formed with at least one radially open hole adjacent this gear. The key has a pinion and a centering pin. The centering pin is fitted into the radially open hole of the chuck body with the pinion meshing with the gear, so that when the key is rotated about the key axis defined by the centering pin and hole and perpendicular to the chuck axis the gear can be forceably angularly displaced with the sleeve about the chuck body. Such an arrangement allows a large mechanical advantage to be applied angularly to the tightening sleeve for tight gripping of a tool between the jaws of the chuck.
Such a system is normally set up for rotary machining or drilling, and the rotation direction of the sleeve is such that during a normal machining operation the force effective on the jaws is in a direction tending to tighten the chuck. For this reason such chucks are normally completely satisfactory for use with most drilling and machining operations.
When, however, such a chuck is to be used on a hammer drill where the tool and the chuck are reciprocated axially while being rotated, loosening can result. Consequently it is normally necessary when using such a hammer drill frequently to retighten the chuck.